Some telecommunications service providers, including cellular and paging companies, provide a "short message service" which allows a user to send and receive displayable messages via a "short message entity." For purposes of this specification, a short message entity is a device that is capable of composing or disposing of short messages. Both wireline and wireless terminals, including cellular telephones and pagers, may function as short message entities. Further, short message service includes the capability of conveying a short message from an originating short message entity to one or more terminating short message entities. For example, current paging systems can transmit a displayable message that consists of a telephone number to be called. Some wireless systems can also send alpha-numeric text for display on the screen of a wireless terminal thus allowing users to send more detailed messages. Alpha-numeric text can also be sent to computing devices such as desk and lap-top computers over wireless or wired terminals or devices. Unfortunately, current short message services can only handle displayable messages of limited size. However, to compete with the burgeoning electronic mail industry, telecommunications service providers would like to be able to transmit longer "short" messages to terminating short message entities.
The Telecommunications Industry Association ("TIA") has prescribed interim standards (designated "IS" concatenated with an identifier) for transmitting displayable messages to short message entities over various wireless air interfaces and networks. Each interim standard specifies a protocol including operations, parameters, operational messages and procedures for transmitting a displayable message as a single data package. For example, IS-95A and IS-637 specify protocols for wireless systems that use Code Division Multiple Access ("CDMA") technology. Further, the IS-136 family of standards specify protocols for short message service in Time Division Multiple Access ("TDMA") systems. The IS-91 family of standards specifies protocols for short message service in advanced mobile phone service ("AMPS/NAMPS") systems. Finally, IS-41-C specifies protocols for short message service over inter-system networks. Analogous protocols exist in the paging industry. Unfortunately, each of these standards specifies a maximum length for the displayable message. The standards do not contemplate transmission of longer displayable messages.
Typically, an originating short message entity generates a displayable message for transmission to a terminating short message entity. The displayable message is transmitted over a "conveying network" or "pipeline" between these short message entities. The conveying network includes the network elements and air interface traversed by the displayable message. The conveying network may include some signaling mechanism such as, for example, Signaling System 7 ("SS7"), X.25, Internet Protocol ("IP"), Asynchronous Transfer Mode ("ATM"), or Frame Relay. Further, the air interface may be digital such as TDMA, CDMA or other digital air interface. Alternatively, the air interface may comprise an analog interface. It is noted that the originating and terminating short message entities do all of the processing with the short message service at the application protocol layer. The intervening conveying network simply acts as a conduit for information between these two end points. Unfortunately, the conveying network can only transmit up to a maximum amount of data or information as a single data package due to, for example, operational standards as described above or specific implementation of portions of the conveying network. The capacity of the conveying network thus limits the size of displayable message that can be transmitted in a data package.
Developers in the paging industry have dabbled with systems that divide a displayable message into multiple fragments for transmission. However, such systems are primitive because there is no method to handle fragments that are received out of order, or to provide for retransmissions to make up for lost fragments. Further, fragmentation of operational messages has been used in lower layer operations in wireless networks. However, to adapt this capability for use in transmitting displayable messages, wireless service providers would have to install numerous software and hardware upgrades to existing networks--an expesive task.